Monarch Butterflies: Special Orienteers!
Every September, hundreds of thousands of Ontario butterflies converge on Point Pelee, a long peninsula which projects south into one of the Great Lakes. Then away they flutter, across the water and far beyond. Thus begins the amazing mass migration of an insect which unerringly navigates 4000 kilometers to a site where these individuals have never been. The Monarch butterfly, it turns out, is an astounding phenomenon.
Spring finds about 100 million Monarch butterflies sunning themselves on huge pine trees in a 150 square kilometer region in the Mexican Sierra Madre mountains. As the days grow longer and warmer, the butterflies which have done little all winter but sit, now start to fly north. Along the way these insects eat newly emerging milkweed plants and lay eggs. The original adults soon die but the next generation emerges and continues the flight north, eating and reproducing as they go. And the next generation does the same thing. At this time of year, the adults live only about a month. Eventually the butterflies reach their summer range in the north central and eastern parts of the United Sates and in south central and eastern Canada. During the summer the butterflies fly aimlessly about, eating and reproducing for perhaps another two generations. These insects have no interest in traveling anywhere specific. Then all of a sudden as the day length declines to only 12 hours of daylight or less, the newly emerging adult butterflies exhibit a compulsion to fly southwest. They fly about 80 km per day for about two months until they reach the site in Mexico which their remote ancestors left so many months previously. The fall hatched butterflies do not reproduce nor do they die after a month. Rather they sit through the winter, waiting for spring to arrive.
In recent years some interesting details concerning the Monarch’s navigation system have emerged. The tiny head of the butterfly makes use of both a clock and a compass to plot the migration route. Even people have a biological clock which they mostly take for granted. How many people wake up at the same time each morning? How many people suffer from jet lag when their biological rhythms are out of synchrony in a new time zone? These effects are produced by a natural internal biological clock. Since Monarch butterflies make such obvious use of a biological clock, this is one of the systems which has been studied. The clock makes use of a daily increase and decline in levels of certain proteins in the tiny butterfly brain.
As daylight arrives, blue light from the sun impacts a light receptor called Cryptochrome (meaning hidden pigment). The light changes the shape of the Cryptochrome 1 in the central complex of the brain (four cells). This protein now has an effect on another protein. It combines with a special protein called Timeless which then begins to decline in amount. At the same time however, Timeless moves into a relationship with Period (also a protein). Period similarly begins to disintegrate but at the same time it moves into a relationship with Cryptochrome 2. It is the latter protein which has the really important effects. It moves into the nucleus of each of these cells and effectively stops production of the clock proteins which are called Clock/Cycle. As these Clock/Cycle proteins decline in amount through the day, the cell takes note of the passage of time. Cryptochrome 2 however has another extremely important effect. It tells the compass what time it is judging by the amount of Clock/Cycle proteins that are left.
As night falls Cryptochrome 1 stops kicking Timeless/Period/Cryptochrome 2, and Cryptochrome 2 then moves out of the nucleus of these brain cells. During the darkness, Clock and Cycle proteins are synthesized, increasing to maximum amounts by daybreak. Also the Timeless and Period and Cryptochrome 2 proteins are synthesized at night. The system goes round and round and it is the arrival of first light in the morning which keeps the clock synchronized with the actual day/night cycle. So scientists have some understanding of part of the butterfly’s navigational system. However there are plenty of other unresolved issues such as the compass.
In order to navigate, of course, one must be able to plot one’s route. The first part of the butterfly’s compass is special cells on the upper rim of each eye. These cells are sensitive to ultra violet light. It is the sensing of these invisible rays coming from the sun, which enable the butterfly to calculate its position relative to the position of the sun in the sky. The butterfly then flies consistently southwest, day after day, week after week to its destination 4000 km away. The butterfly knows where the southwest is, based on the sun’s position in the sky. But of course the sun is constantly changing its position, as it moves from east to west across the sky. This is where the biological clock becomes important. It tells the compass what time it is so that the butterfly can constantly adjust its angle of flight compared to the sun’s position .
Studies with butterfly flight patterns show that the butterflies fly obliquely away from the sun (towards the SW) in the morning when the sun is in the east, and obliquely toward the sun (towards the SW) in the afternoon when the sun is in the west. If the butterfly’s schedule is artificially manipulated so that it thinks 7 a.m. is actually 1 p.m., then the butterfly flies SE (towards the sun) instead of away from it as it should do in the morning. It is evident that the butterfly’s navigation system of clock and compass is like two gears moving in opposite directions against each other. A new study released in September 2009 however suggests that the biological clock, which interacts with the compass, is actually located in the butterfly antennae. So the insect must have two clocks!
Another topic that interests biologists about these insects, is the degree to which the navigational system is unique. The short answer is extremely unusual! A news item in Medical News Today (January 9/08) declared that scientists were “stunned and elated” to discover how unusual the Monarch butterfly biological clock is. Previous studies on the fruit fly and mouse had led scientists to suspect that the Monarch’s system would resemble that of the fruitfly (another insect). What they found however was a “novel molecular mechanism heretofore not found in any other insect or mammal” according to Medical News Today). As the authors of the study report: “The expression of two functionally distinct crys [Cryptochromes] in monarchs suggests that the butterfly clock may use a novel clockwork mechanism that is not yet fully described in any organism.” (Haisan Zhu et al. PLoS Biology 6 (1): p 3 of 30).
Thus the Monarch’s biological clock seems to be unique among insects and all studied organisms. Scientists who might try to find evolutionary sources for this system will have a difficult time. There are no obvious lines of descent from similar organisms. And of course biologists have not even begun to figure out how the compass works. No doubt the uniquely designed status of the Monarch will become even more apparent as the workings of the compass are uncovered.
As we look about us at even small organisms in nature like the Monarch butterfly, let us reflect on the exquisite design of these delightful organisms. Let us then ascribe praise to the Creator of all things.
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